Zoom lens and imaging apparatus

Abstract

A zoom lens consists of five lens groups including, in order from the object side, positive, negative, positive, positive, and positive lens groups. During magnification change, the first and fifth lens groups are fixed relative to the image plane, and the second, third, and fourth lens groups are moved to change distances therebetween. During magnification change from the wide-angle end to the telephoto end, the second lens group is moved from the object side toward the image plane side, and the fourth lens group is moved from the image plane side toward the object side. The fifth lens group includes at least two negative lenses, and satisfies the condition expression (1) below: 1.90< LABnd   (1).

What is claimed is: 
     
       1. A zoom lens consisting of, in order from an object side, a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, a fourth lens group having a positive refractive power, and a fifth lens group having a positive refractive power,
 wherein, during magnification change, the first lens group and the fifth lens group are fixed relative to an image plane, and the second lens group, the third lens group, and the fourth lens group are moved to change distances therebetween, 
 during magnification change from a wide-angle end to a telephoto end, the second lens group is moved from the object side toward the image plane side, and the fourth lens group is moved from the image plane side toward the object side, 
 the fifth lens group comprises at least two negative lenses, and 
 the condition expression (1) below is satisfied:
   1.90< LABnd   (1),
 
 
 
       where LABnd is an average value of a refractive index LAnd with respect to the d-line of an LA negative lens, which is the first negative lens from the image plane side of the fifth lens group, and a refractive index LBnd with respect to the d-line of an LB negative lens, which is the second negative lens from the image plane side of the fifth lens group. 
     
     
       2. The zoom lens as claimed in  claim 1 , wherein the condition expression (2) below is satisfied:
   0.42< LAnd−LCnd   (2),
 
 
       where LCnd is a refractive index with respect to the d-line of an LC positive lens, which is the first positive lens from the image plane side of the fifth lens group. 
     
     
       3. The zoom lens as claimed in  claim 1 , wherein the condition expression (3) below is satisfied:
   25< LABνd< 40  (3),
 
 
       where LABνd is an average value of an Abbe number LAνd with respect to the d-line of the LA negative lens and an Abbe number LBνd with respect to the d-line of the LB negative lens. 
     
     
       4. The zoom lens as claimed in  claim 1 , wherein the second lens group consists of, in order from the object side, an L 21  negative lens, an L 22  negative lens, a cemented lens formed by an L 23  negative lens having a biconcave shape and an L 24  positive lens which are cemented together in this order from the object side, a cemented lens formed by an L 25  positive lens with a convex surface toward the image plane side and an L 26  negative lens with a concave surface toward the object side which are cemented together in this order from the object side. 
     
     
       5. The zoom lens as claimed in  claim 4 , wherein the condition expression (4) below is satisfied:
     L 23ν d−L 24ν d<L 26ν d−L 25ν d   (4),
 
 
       where L23νd is an Abbe number with respect to the d-line of the L 23  negative lens, L24νd is an Abbe number with respect to the d-line of the L 24  positive lens, L26νd is an Abbe number with respect to the d-line of the L 26  negative lens, and L25νd is an Abbe number with respect to the d-line of the L 25  positive lens. 
     
     
       6. The zoom lens as claimed in  claim 1 , wherein the first lens group consists of, in order from the object side, an L 11  negative lens, an L 12  positive lens, an L 13  positive lens, an L 14  positive lens, and an L 15  positive lens. 
     
     
       7. The zoom lens as claimed in  claim 1 , wherein an L 21  negative lens, which is the most object-side negative lens of the second lens group, satisfies the condition expression (5) below:
   25<ν d 21<45  (5),
 
 
       where νd21 is an Abbe number with respect to the d-line of the L 21  negative lens. 
     
     
       8. The zoom lens as claimed in  claim 1 , wherein the condition expression (1-1) below is satisfied:
   1.94< LABnd   (1-1).
 
 
     
     
       9. The zoom lens as claimed in  claim 2 , wherein the condition expression (2-1) below is satisfied:
   0.45< LAnd−LCnd   (2-1).
 
 
     
     
       10. The zoom lens as claimed in  claim 3 , wherein the condition expression (3-1) below is satisfied:
   30< LABνd< 36  (3-1).
 
 
     
     
       11. The zoom lens as claimed in  claim 7 , wherein the condition expression (5-1) below is satisfied:
   28<ν d 21<40  (5-1).
 
 
     
     
       12. An imaging apparatus comprising the zoom lens as claimed in  claim 1 .